1. Field of the Invention
The present invention relates to a process and a catalyst for the production of diaryl carbonates, and more particularly to a process and a homogeneous catalyst for the homogeneous liquid phase reaction of aromatic haloformates with aromatic hydroxy compounds for the production of diaryl carbonates with the elimination of anhydrous hydrogen halide.
2. Description of the Related Art
Prior art methods for the production of diaryl carbonates have used the interfacial route involving a two phase reaction system and various homogeneous catalytic systems. The interfacial route involves the neutralization of the aromatic hydroxy compound with caustic and the subsequent reaction of an aqueous solution of the phenate type salt of the aromatic hydroxy compound with a carbonyl halide usually phosgene. In the case where the desired product is diphenyl carbonate, excess caustic to insure the complete neutralization of phenol results in a loss of about 20 percent of the phosgene. Salt which represents the loss of two chlor/alkali equivalents is produced. As a consequence, the aqueous stream coming from this reaction process requires treatment prior to disposal. Caustic equivalents include the group 1, 2, 11 and 12 hydroxides, oxides, carbonates and phosphates.
The prior art alternatives to the above described interfacial route to diaryl carbonates are various homogeneous catalytic processes. U.S. Pat. No. 2,362,865 discloses the use of metal phenates as catalysts in the reaction of phenol and phosgene to form diphenyl carbonate in a process in which the phenol is in the liquid phase. U.S. Pat. Nos. 3,234,261 and 3,234,263 relate to the formation of diaryl carbonates from various chloroformates by reaction with metal oxides, with the process of the '263 patent employing a tertiary amine base as a catalyst. Related processes are disclosed in French Pat. No. 1,361,228 and U.S. Pat. No. 3,251,873.
U.S. Pat. No. 4,012,406 discloses a process for the preparation of diaryl carbonates by the reaction of aromatic monohydroxy compounds with phosgene with the aid of an aromatic heterocyclic basic nitrogen compound as a catalyst. Such catalysts are effective for the conversion of haloformates and aromatic hydroxy compounds into diaryl carbonates as would be expected since a haloformate is an intermediate in the reaction of an aromatic hydroxy compound and phosgene to form the same product.
A process for the reaction of aromatic hydroxy compounds with carbonyl halides to produce diaryl carbonates which employs a heterogeneous catalyst system is described in U.S. Pat. application Ser. No. 429,954 filed on Oct. 30, 1989, now abandoned, and refiled as U.S. Ser. No. 07/682,400, filed Apr. 5, 1991, by Harley et.al.
The use aromatic heterocyclic basic nitrogen compounds as catalysts for the reaction of an aromatic haloformate with an aromatic hydroxy compound which is carried out in an inert reaction medium is described in U.S. Pat. application Ser. No. 451,893, filed Dec. 18, 1989, now abandoned, and refiled as U.S. Ser. No. 07/739,778, filed Jul. 30, 1991.
U.S. Pat. No. 4,366,102 discloses a process which employs various organic phosphorus compounds as catalysts for the reaction of a phenol and phosgene to form an aromatic chloroformic ester. This patent teaches that numerous advantages are derived from the use of the catalysts described therein. This patent also teaches that it is surprising that the organic phosphorus compounds of the disclosed process catalyze the reaction to form the ester, but do not promote the further condensation to form the diaryl carbonate.